1. Field of the Invention
This invention relates to a manufacturing method for a ferroelectric thin film, a manufacturing method for a ferroelectric element, a surface acoustic wave element, a frequency filter, an oscillator, an electronic circuit, and an electronic apparatus.
Priority is claimed on Japanese Patent Application No. 2003-85760, filed Mar. 26, 2003, the content of which is incorporated herein by reference.
2. Description of Related Art
Ferroelectric elements having a ferroelectric thin film are used in various types of devices, such as ferroelectric memories, thin film capacitors, sensors, surface acoustic wave elements, filters, optical waveguides, optical memory devices, space light modulators, piezoelectric actuators, and the like. The capabilities of these types of devices vary according to the quality of the ferroelectric thin film in the ferroelectric element in particular. For this reason, the ferroelectric thin film should ideally be an epitaxial film.
Recently there are demands for integrating ferroelectric elements and semiconductor elements in devices such as ferroelectric memories, for instance. Since ferroelectric materials have piezoelectric characteristics, the ferroelectric film becomes a piezoelectric film, and the ferroelectric element functions as a piezoelectric element.
For example, as disclosed in Japanese Unexamined Patent Application, First Publication Nos. 2001-107238 and 2002-76294, when attempting to obtain alignment film or epitaxial film for a ferroelectric thin film, it is necessary to use a special single crystal substrate including an Si substrate.
In view of the cost and wide range of applications of ferroelectric elements, it is desirable to use a substrate that is less expensive than the single crystal substrate (e.g. an amorphous or plastic substrate) for forming the ferroelectric thin film. In this case, however, there is a problem in that the ferroelectric thin film is inadequate in quality, for such reason as it is not possible to grow epitaxially or the like, with the result that the characteristics of the ferroelectric element obtained from it are also inadequate.
When integrating a ferroelectric element with a semiconductor element, the ferroelectric element must be formed on the interlayer insulating film and the protective film, but since these are generally amorphous, it is difficult to grow ferroelectric thin film epitaxially on them. The element must be heated to a temperature of higher than 600° C. in order to form the ferroelectric thin film; however, when attempting to form this ferroelectric thin film on the semiconductor element, there is a danger of damage to the semiconductor element, such as deterioration in its characteristics due to the heat. Moreover, the constituent elements of the ferroelectric thin film include alkali metal, alkaline earth metals, and volatile elements, which semiconductor elements do not like; this considerably restricts the manufacturing process, since the ferroelectric thin film cannot be heated to high temperature.
This invention has been realized in consideration of the problems described above, and aims to provide methods for manufacturing a ferroelectric film and a ferroelectric element, which make it possible to form a high-performance ferroelectric element on any substrates, thereby facilitating the integration of the ferroelectric element with a semiconductor element, a surface acoustic wave element that uses the ferroelectric film and the ferroelectric element, manufactured according to these manufacturing methods, a frequency filter, an oscillator, an electronic circuit, and an electronic apparatus, each of which uses the surface acoustic wave element.